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If their relative velocity is only radial, they must eventually crash into one another, even if they begin moving apart.
PhractQuote from: Phractality on 05/06/2011 20:34:31If their relative velocity is only radial, they must eventually crash into one another, even if they begin moving apart.Agree - other than fact that if the radial velocity apart is greater than the escape velocity, which for two particles of a gram 10^7 m apart would not be very high (to the order of 10^-10 m/s).
I must admit I struggled to get straight in my head how to quantify the intrinsic expansion of space and see if this would have an effect. I would be interested to see if you came to a conclusion.
Vajira Kashyapa asked the Naked Scientists: Dear Naked Astronomy,Your postcast is brilliant! I have been listening since 1st episode. I have a follow up question regarding an answer given to a listener questions your last episode (May 25th).---------Original Question: A listener asked the questions, If you place two particles of mass in an empty universes, would they actually attract each other and move closer together and collide?Original Answer: Yes, if u take an example of 1gram particles, set 10000KM apart from each other they would move towards each other as long as they were completely stationary.---------My questions is: Would the particles not stay completely stationary, if the same mass particles started out completely stationary to each other, and at an equal distance away from each other?My thinking regarding this is: If you place two stationary objects of equal mass, at equal distance from each other, would they not stay the same unless one or both particles are forced to either not stay stationary or are increased in mass or increased in distance? If you were to have two skaters of equal mass spinning around each other at a constant speed, and they are not acted upon by any other force, they will continue to spin until a force acts upon them, They will not collide into each other.Vajira Kashyapa - From Sri Lanka What do you think?